This invention relates to room temperature curable organopolysiloxane compositions, and more particularly, to room temperature curable organopolysiloxane compositions which are adherent to difficult-to-bond resins used as sealants or for bonding and securing of electric and electronic parts.
Various types of room temperature curable organopolysiloxane compositions are well known in the art which cure into elastomers at room temperature upon contact with air-borne moisture. Among others, those compositions of the type that cure while releasing alcohol are preferentially used in sealing, bonding and coating of electric and electronic equipment, owing to their advantageous features of no disgusting odor and no corrosion of metals. One typical composition of this type is described in JP-B 39-27643 as comprising an organopolysiloxane end-blocked with hydroxyl groups, an alkoxysilane, and an organic titanium compound. Also JP-A 55-43119 discloses a composition comprising an organopolysiloxane end-blocked with alkoxysilyl groups, an alkoxysilane, and alkoxy titanium. JP-B 7-39547 discloses a composition comprising an organopolysiloxane end-blocked with alkoxysilyl groups (including silethylene), an alkoxysilane, and alkoxy titanium. JP-A 62-207369 discloses a composition comprising an alkoxysilyl end-capped organopolysiloxane, a hydroxyl-terminated organopolysiloxane, an alkoxysilane and titanium. Allegedly improvements are made in resistance to oil swelling and shelf life. For these compositions of the type that cure while releasing alcohol, engineers have made efforts to improve the preparation method, shelf stability (suppression of changes with time) and various properties, typically resistance to oil swelling. Although the above-referred compositions appear analogous, the individually specified composition has an important meaning in positively acquiring the desired set of properties.
Meanwhile, with the sophistication of techniques of improving the durability of resins, many of the resins currently used in housings of electric and electronic appliances are not bondable with conventional sealants. The above-referred compositions used for sealing, bonding and coating in electric and electronic equipment are not fully adherent to these resins.
An object of the invention is to provide a room temperature curable organopolysiloxane composition which is fully adherent to difficult-to-bond resins used as sealants or for bonding and securing of electric and electronic parts. We have found that by using an organopolysiloxane having at least two organooxysilyl groups in a molecule as a base polymer, and adding thereto specific amounts of a hydroxyl end-capped organopolysiloxane, an organooxysilane or partial hydrolytic condensate thereof, and a titanium chelate catalyst, there is obtained an organopolysiloxane composition which has shelf stability and is dramatically improved in adhesion to those resins which are believed to be difficult to bond. The present invention is predicated on this finding.
Accordingly, the present invention provides a room temperature curable organopolysiloxane composition comprising components (A) to (D):
(A) 100 parts by weight of an organopolysiloxane having at least two organooxysilyl groups in a molecule, represented by the following general formula (1) or average formula (2) or (3): 
wherein R1 is a monovalent hydrocarbon group, R2 is a monovalent hydrocarbon group or alkoxy-substituted monovalent hydrocarbon group, R3 is a substituted or unsubstituted monovalent hydrocarbon group, Y is an oxygen atom or divalent hydrocarbon group having 1 to 8 carbon atoms, b is an integer of 1 to 3, c, d, e and m each are an integer of at least l, k is an integer of at least 2, and c, d+m and e+k in the formulae are each such an integer that the organopolysiloxane has a viscosity of 20 to 1,000,000 centipoises at 25xc2x0 C.,
(B) 1 to 30 parts by weight of a hydroxyl-terminated linear organopolysiloxane having the following general formula (4): 
wherein R3 is substituted or unsubstituted monovalent hydrocarbon group and f is such an integer that the organopolysiloxane has a viscosity of 20 to 1,000,000 centipoises at 25xc2x0 C.,
(C) 0.5 to 15 parts by weight of an organooxysilane having the general formula: R1aSi(OR2)4-a wherein R1 is a monovalent hydrocarbon group, R2 is a monovalent hydrocarbon group or alkoxy-substituted monovalent hydrocarbon group, and xe2x80x9caxe2x80x9d is 0 or 1, or a partial hydrolytic condensate thereof, and
(D) 0.1 to 10 parts by weight of a titanium chelate catalyst.
The room temperature curable organopolysiloxane composition is arrived at by using as a base polymer an organopolysiloxane having per molecule at least two silicon atoms each attached to an organooxy group through an oxygen atom or divalent hydrocarbon group and compounding therewith specific amounts of a hydroxyl end-capped organopolysiloxane, an organooxysilane or partial hydrolytic condensate thereof, and a titanium chelate compound as a catalyst.
Component (A), which serves as a base polymer of the inventive composition, is an organopolysiloxane having per molecule at least two, preferably 2 to 10 silicon atoms each attached to an organooxy group, especially alkoxy group through an oxygen atom or divalent hydrocarbon group. Namely, component (A) is one or more organooxysilyl group-containing organopolysiloxanes having the following general formula (1), average formula (2) and average formula (3). It is noted that the average formula means that siloxane units having pendant alkoxy groups may be discretely dispersed rather than being blocked together. 
Herein R1 is a monovalent hydrocarbon group, R2 is a monovalent hydrocarbon group or an alkoxy-substituted monovalent hydrocarbon group, R3 is a substituted or unsubstituted monovalent hydrocarbon group, Y is an oxygen atom or divalent hydrocarbon group having 1 to 8 carbon atoms, b is an integer of 1 to 3, c, d, e and m each are an integer of at least l, k is an integer of at least 2, and c, d+m and e+k in the formulae are each such an integer that the organopolysiloxane has a viscosity of 20 to 1,000,000 centipoises at 25xc2x0 C.
In the organopolysiloxanes of the general formula (1) or the average formula (2) or (3), the monovalent hydrocarbon groups represented by R1 and R3 are preferably unsubstituted or substituted (halogen, cyano or otherwise substituted) monovalent hydrocarbon groups having 1 to 12 carbon atoms, especially 1 to 10 carbon atoms, for example, alkyl groups such as methyl, ethyl, propyl, butyl, hexyl, octyl, decyl, and octadecyl, cycloalkyl groups such as cyclopentyl and cyclohexyl, alkenyl groups such as vinyl and allyl, aryl groups such as phenyl, tolyl and naphthyl, and aralkyl groups such as benzyl, phenylethyl and phenylpropyl. Exemplary of halogenated hydrocarbon groups are chloromethyl, trifluoromethyl, chloropropyl, 3,3,3-trifluoropropyl, chlorophenyl, dibromophenyl, tetrachlorophenyl, and difluorophenyl. Exemplary of cyanoalkyl groups are xcex2-cyanoethyl, xcex3-cyanopropyl and xcex2-cyanopropyl. Of these, methyl is most preferred.
For R2, hydrocarbon groups of 1 to 10 carbon atoms, especially 1 to 4 carbon atoms are preferred. Examples of suitable monovalent hydrocarbon groups are as described above. Typical examples include alkyl groups such as methyl, ethyl, propyl, butyl, hexyl and octyl, and alkoxy-substituted alkyl groups such as methoxyethyl, ethoxyethyl, methoxypropyl and methoxybutyl. Of these, methyl and ethyl are most preferred.
Desirably, each of R1, R2 and R3 has 1 to 3 carbon atoms, and is most desirably methyl.
Y is an oxygen atom or a divalent hydrocarbon group. Suitable divalent hydrocarbon groups are alkylene groups having 1 to 8 carbon atoms, especially 1 to 6 carbon atoms, such as xe2x80x94CH2CH2xe2x80x94, xe2x80x94CH2CH2CH2xe2x80x94 and xe2x80x94CH2C(CH3)Hxe2x80x94, with xe2x80x94CH2CH2xe2x80x94being most preferred.
The subscripts b, m and k are as defined above, b is preferably 2 or 3, m is preferably 1 to 10, more preferably 1 to 5, most preferably 1 to 3, and k is preferably 2 to 10, more preferably 2 to 6, most preferably 2 to 4. If values of m and k are too large, the cured product may have insufficient rubber elasticity.
The organopolysiloxane (A) should have a viscosity of 20 to 1,000,000 centipoises at 25xc2x0 C. With a viscosity of less than 20 cp, the elastomer as cured may not have satisfactory physical properties, especially flexibility and elongation. With a viscosity of more than 1,000,000 cp, the composition may have too high a viscosity to apply. The preferred viscosity is in the range of 100 to 500,000 cp. Accordingly, n, d+m and e+k are selected such that the viscosity of the organopolysiloxane may fall in the desired range.
The organopolysiloxane (A) containing per molecule at least two organooxysilyl groups attached to silicon atoms through an oxygen atom or divalent hydrocarbon group can be prepared by prior art well-known methods. For example, the organopolysiloxane (A) is prepared by effecting addition reaction between a corresponding alkenyl group-terminated organopolysiloxane and an organooxysilane having the following formula (6): 
wherein R1, R2 and b are as defined above in the presence of a Pt catalyst. Alternatively, addition reaction is effected between a corresponding SiH-terminated organopolysiloxane and a silane of the following formula (7): 
wherein R4 is an alkenyl group, R1, R2 and b are as defined above.
Component (B) is crucial for imparting resin adhesiveness as intended in the present invention. It is a linear organopolysiloxane having a hydroxyl group at an end, represented by the following general formula (4): 
wherein R3 is substituted or unsubstituted monovalent hydrocarbon group and f is such an integer that the organopolysiloxane has a viscosity of 20 to 1,000,000 centipoises at 25xc2x0 C.
In formula (4), R3 is as exemplified for R3 in component (A). The organopolysiloxane (B) should have a viscosity at 25xc2x0 C. of 20 to 1,000,000 centipoises, preferably 100 to 500,000 centipoises. With too low a viscosity, the organopolysiloxane (B) imparts insufficient adhesion. With too high a viscosity, the composition becomes awkward to process.
Component (B) is added in an amount of 1 to 30 parts by weight, preferably 5 to 20 parts by weight per 100 parts by weight of component (A). With too much component (B), the composition has poor shelf stability or changes with time. Too small amounts of component (B) fail to impart adhesion to difficult-to-bond resins.
Component (C) serves as a crosslinker for helping the composition cure into a rubber elastomer. It is an organooxysilane having the following general formula or a partial hydrolytic condensate thereof.
R1aSi(OR2)4-a
Herein R1 is a monovalent hydrocarbon group, R2 is a monovalent hydrocarbon group or alkoxy-substituted monovalent hydrocarbon group, and xe2x80x9caxe2x80x9d is 0 or 1.
Examples of the monovalent hydrocarbon group or alkoxy-substituted monovalent hydrocarbon group represented by R1 and R2 are the same as illustrated above for component (A).
Illustrative examples of the organooxysilane (C) include tetrafunctional alkoxysilanes such as tetramethoxysilane, tetraethoxysilane and methylcellosolve orthosilicate; trifunctional alkoxysilanes such as methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, vinyltrimethoxysilane, phenyltrimethoxysilane and methyltrimethoxyethoxysilane, and partial hydrolytic condensates thereof. These organooxysilanes may be used alone or in admixture of any. In order to impart low modulus to rubber elastomers after curing, difunctional alkoxysilanes such as diphenyldimethoxysilane and dimethyldimethoxysilane may be additionally added.
Component (C) is generally added in amounts of 0.5 to 15 parts by weight, preferably 1 to 10 parts by weight, per 100 parts by weight of component (A). With too small amounts of component (C), the composition may not fully cure and tends to thicken and gel during storage in a cartridge. Too large amounts of component (C) may retard curing, provide unsatisfactory rubber physical properties and be uneconomical.
Component (D) is a catalyst for the inventive composition to cure. Exemplary catalysts include organotitanium compounds such as tetraisopropoxytitanium, tetra-t-butoxytitanium, titanium diisopropoxide bis(ethyl acetoacetate), and titanium diisopropoxide bis(acetylacetonate); organotin compounds such as dibutyltin dilaurate, dibutyltin bisacetylacetonate and tin octylate; metal salts of dicarboxylic acids such as lead dioctylate; organozirconium compounds such as zirconium tetraacetylacetonate; organoaluminum compounds such as aluminum triacetylacetonate; and amines such as hydroxylamine and tributylamine. Of these, organotitanium compounds are preferred. Titanium chelate catalysts are most preferred for enhancing the storage stability of the inventive composition. Typical titanium chelate catalysts are of the general formulae (8) and (9). 
Herein, X is a monovalent hydrocarbon group, alkoxy or amino group, R1, R2 and R3 are as defined above, and p is an integer of 1 to 8.
The monovalent hydrocarbon groups represented by X are exemplified by monovalent hydrocarbon groups of 1 to 12 carbon atoms, especially 1 to 10 carbon atoms, as described above for R1 and R3. Preferred alkoxy groups are those of 1 to 8 carbon atoms, especially 1 to 6 carbon atoms. R1 and R3, taken together, may form a ring having 5 to 8 carbon atoms in total with the Cxe2x95x90C to which they are attached.
Illustrative examples of titanium chelate catalysts (D) include titanium diisopropoxide bis(ethyl acetoacetate), titanium diisopropoxide bis(acetylacetone), titanium dibutoxide bis(methyl acetoacetate), and those of the formulae shown below. 
Component (D) is generally added in catalytic amounts, preferably amounts of 0.1 to 10 parts by weight, preferably 0.2 to 7 parts by weight, per 100 parts by weight of component (A). With too small amounts of component (D), the composition will slowly cure. With too large amounts of component (D), the composition will cure too fast and become unstable during storage.
In the inventive composition, (E) a trimethylsiloxy-terminated linear organopolysiloxane having the following general formula (5) is preferably compounded for the purpose of controlling the fluidity of the composition prior to curing or adjusting the modulus of the rubber elastomer after curing. 
Herein R3 is substituted or unsubstituted monovalent hydrocarbon group, g is such an integer that the organopolysiloxane has a viscosity of 20 to 1,000,000 centipoises at 25xc2x0 C., and Me is methyl.
Examples of the substituted or unsubstituted monovalent hydrocarbon group represented by R3 are the same as exemplified for R3 in component (A).
The organopolysiloxane (E) has a viscosity of 20 to 1,000,000 centipoises at 25xc2x0 C. With a viscosity of less than 20 cp, the cured elastomer may not be endowed with satisfactory physical properties, especially flexibility and elongation. With a viscosity of more than 1,000,000 cp, the composition may have too high a viscosity, substantially detracting from efficiency upon application. The preferred viscosity is in the range of 100 to 500,000 cp. Therefore, g is selected such that the viscosity may fall in the desired range.
Component (E) is added in an amount of 1 to 50 parts by weight, preferably 5 to 40 parts by weight per 100 parts by weight of component (A). Too small amounts may fail to provide the addition effect whereas too large amounts may have negative impact on the impartment of adhesion.
In a preferred embodiment of the invention, the composition further includes (F) fumed silica. It is a component for reinforcement, i.e., increasing the mechanical strength of cured rubber elastomers.
The fumed silica should preferably have a BET specific surface area of at least 10 m2/g, and more preferably 50 to 400 m2/g, and be added in amounts of 1 to 40 parts by weight, preferably 2 to 30 parts by weight, per 100 parts by weight of component (A).
The fumed silica may be either hydrophobic silica or hydrophilic silica, which may be used alone or in combination. The hydrophobic silicas are typically ones treated with organosilicon compounds having dialkylsilyl or trialkylsilyl groups. Most preferably, silica is treated with hexamethyldisilazane or the like so that trimethylsilyl groups are bound to silica surfaces although surface treatment with dimethyldichlorosilane, cyclic dimethylsiloxane, hydroxyl-containing dimethyloligosiloxane or the like is acceptable. A mixture of two or more hydrophobic silicas is also useful.
In the inventive composition comprising components (A) to (F) described above, a fine powder inorganic filler may optionally be added for the purposes of improving flow characteristics prior to curing and endowing the cured rubber elastomer with desired mechanical properties. Examples of the inorganic filler include quartz flour, calcium carbonate, fumed titanium dioxide, diatomaceous earth, aluminum hydroxide, microparticulate alumina, magnesia, zinc oxide and zinc carbonate, which may be surface treated with silanes, silazanes, low degree-of-polymerization siloxanes, and organic compounds.
Furthermore, organic solvents, mildew-proofing agents, flame retardants, heat resistance modifiers, plasticizers, thixotropic agents, adhesion promoters, curing promoters, pigments and the like may be added to the inventive composition as long as they do not compromise the objects of the invention.
The inventive composition may be prepared by mixing components (A) to (F) and optional additives under humidity-shielded conditions. The composition thus obtained is stored in a sealed container, typically cartridge and on use, exposed to air-borne moisture whereupon it cures into a rubbery elastomer. That is, the inventive composition can be used as one part type RTV organopolysiloxane composition.
The organopolysiloxane composition of the invention is fully adherent to difficult-to-bond resins which are used as sealants or for bonding and securing of electric and electronic parts.
On account of improved water resistance and moisture resistance, the inventive composition is compatible with many applications including coating materials requiring water resistance, such as ship bottom paint, power plant seawater inlet pipe paint, and fishing net paint; moisture-proof coating materials requiring moisture resistance as used in LCD and PDP; and adhesive seals between conductors and resin coatings, adhesive seals between conductors and resin casings or resin connectors, and adhesive seals for reduced or increased pressure chambers.
In building applications requiring moisture resistance and water resistance, the inventive composition is useful as adhesive seals between rubber gaskets and glazing, joint seals for double-glazed units, adhesive seals at joints and edges of water-proof sheets, adhesive seals between solar water heating units and roof water-proof sheets, adhesive seals between solar battery panels and roofing, and face bonds between siding panels and walls.
The inventive composition is also applicable as adhesive seals between window glass or transparent resin plates and frames of meters and other instruments.